DESCRIPTION This proposal will investigate mechanisms that degrade platelet-activating factor (PAF) in intestinal tissue during episodes of pathophysiological stress. Excessive PAF accumulation and PAF-signaling in intestinal tissue promotes leukocyte infiltration and subsequently cellular damage. PAR- acetylhydrolase (AH) is the enzyme responsible for PF degradation and PAF-AH activity has recently been detected in the bile and intestinal tissue. This proposal will examine the following issues: 1) the role of the biliary PAF-AH in controlling PAF levels in the intestine; 2) examination of the expression and regulation of endogenous intestinal PAF-AH. Initially, characterization of the biliary PAF-AH will involve identification of the protein using mass spectrometry and amino acid sequence analysis to elucidate its molecular identity. The cellular source of biliary PAF-AH will be examined in primary hepatic cell cultures using enzymatic and immunological techniques. Hepatic adaptive responses to in vivo intestinal inflammatory models will be evaluated by measuring biliary PAF-AH activity and intestinal PAF-AG to the mucosal surface may be an important mechanism for controlling PAF levels in the intestinal tissue. Endogenous intestinal protease resistant PAF-AH expression and localization will be examined using in vivo inflammation models and primary enterocyte culture. Correlation between tissue PAF levels, endogenous PAF-AH expression and leukocyte infiltration will be investigated in these models. Endogenous PAF-AH expression will be analyzed using in situ hybridization and immunohistochemical analyses of intestinal tissue. Distinct intestinal regions have a propensity to become inflamed suggesting excessive production of PAF and PAF-signaling and/or failure to regulate PAF levels appropriately. Examination of hepatic and intestinal PAF-AH production and activity will provide valuable insight concerning intestinal pathophysiology.